1. Field of the Invention
The present invention relates to a driving device that is used to drive a display such as a liquid crystal display.
2. Description of the Prior Art
First, a conventional driving device designed to drive a display will be described with reference to FIG. 11. FIG. 11 is a block diagram of a display apparatus that achieves screen display on a display 60 that is controlled by a microcomputer 62 through a driver IC (integrated circuit) 61.
This display apparatus also has a character ROM (read-only memory) 63 in which characters such as letters and symbols to be displayed are stored. The microcomputer 62 reads from the character ROM 63 the data of the characters it is going to display, and stores the obtained character data in a RAM (random-access memory) provided within the microcomputer 62. The microcomputer 62 then outputs this character data, as bit-mapped display data, to the driver IC 61. The driver IC 61 then produces a driving signal in accordance with this display data, and feeds the produced driving signal to the display 60 to display the desired characters thereon.
Accordingly, to display characters on the display 60, the microcomputer 62 needs to access first the character ROM 63, to read the corresponding data therefrom, and then the driver IC 61. As a result, in this display apparatus employing a conventional driver IC 61, the microcomputer 62, which needs to access the driver IC 61 as frequently as it needs to access the character ROM 63, is required to operate at an accordingly high rate, and thus tends to suffer from unduly high electric current consumption.
Moreover, with the development of larger and larger display systems, the size of the display 60 as well as the number of characters stored in the character ROM 63 tends to increase. This leads not only to an increase in the number of addresses used to specify characters, but also to an increase in the number of characters that are displayed on the display 60 at a time. As a result, the microcomputer 62 needs to read more character data from the character ROM 63, and thus it needs to access the character ROM 63 more frequently; on the other hand, the microcomputer 62 outputs more display data, and thus it needs to access the driver IC 61 more frequently. In this way, with the development of larger and larger display systems, the microcomputer 62, which needs to access both the driver IC 61 and the character ROM 63 more frequently, is required to operate at an even higher rate, and thus suffers from even higher electric current consumption.
Moreover, in the above-described display apparatus, to achieve refreshing, such as scrolling, of what is displayed on the screen, the microcomputer 62 first needs to access the character ROM 63 to read therefrom the display data of the characters to be scrolled and store the obtained data in the above-mentioned RAM in a way that corresponds to the state of the screen after the scrolling; then, the microcomputer 62 needs to output the bit-mapped data for the entire screen to the driver IC 61. In this way, to achieve the scrolling of the characters read from the character ROM 63, the microcomputer 62 needs to access the character ROM 63 still more frequently, and is thus required to operate at a still higher rate.